Electron-discharge device.



w. I). commit ELECTRON DISCHARGI DEVICE.

APPLICATION FILED JUNE 13 1916.

Patented Apr. 2, 1918.

Inventor: William D. Coolidge,

His fitto rney.

.. era PATENT onmcn.

WILLIAM D. COOLIDGE, OF SOHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRON-DISCHARGE DEVICE.

To all whom it may concern Be it known that I, WILLIAM D. Coomnen, acitizen of the United States, residin at Schenectady, county ofSchenectady, tate of New York, have invented certain new and usefulImprovements in Electron-Discharge Devices, of which the following is aspecification.

The present invention relates to electron discharge devices, andparticularly to a device for the generation of X-rays.

In accordance with my invention, I have provided a device operable witha substantially ure electron discharge comprising a metallic body partpreferably acting also as anode, and an insulating part into which thecathode conductors are sealed, the two parts being joined to each other,and means being provided to prevent the accumulation of an electric'charge near the joint. In the described embodiment of my invention thismeans is a conductive member extending within the tube from the metalpart past the joint between the twoparts. The constricted space betweenthe conductive member and the cathode tube-wall prevents theaccumulation of harmful electrostatic stresses at the joint as Will behereinafter more fully explained.

In the accompanying drawing, Figure 1 is a longitudinal section of anX-ray tube embodying my invention, and Fig. 2 is a longitudinal sectionof a modification.

The device shown in Fig. 1 comprises an envelop consisting of aninclosure 1 of metal, as, for example, copper, and an inclosure 2, ofinsulating material such as glass. A section 3 of platinum is welded orsoldered to the copper wall at 4 and is sealed to the glass wall at 5. Atube 6 consisting of copper, or other suitable metal is welded, orotherwise joined, to the tube 1 at 4 and extends into the insulatingpart 2 of the envelop past the joint 5.

The cathode comprises a coiled filamentary conductor 7 consistingpreferably of tungsten, this being shown on edge. Surrounding thefilament is a tube 8, of mol bdenum, or other suitable conductivematerial,

acting as a focusing device. One end of the cathode filament is joinedto the focusing device and the other end to a conductor 9. Joined to thetube 8 are two wires 10 and 11 which are secured to a split tube 12 ofSpecification of Letters l atent.

Patented Apr. 2, 1918.

Application flied June 13, 1916. Serial No. 103,557.

11 are bound together by a bridge 13, suitable insulation being used ifthe bridge consists of conducting material. The wires 9 and 10 aresealed into the closed end of the tube section 2. The cathode structureis carried by a tube 14. of glass, or other suitable insulatingmaterial.

Within the mctal end 1 ofgthe device is applied an anode plate, ortarget 15, consisting of tungsten or other suitable refractory metal.The target is cooled by water, air, or other suitable cooling fluidcirculating through a chamber back of the anode into the wall of whichare sealed tubes 16 and 17 for supplying and Withdrawing the coolingfluid. Opposite the anode is a tube 18 closed with a window 19 of thinmetal, glass, or other material relatively transparent to X-rays.

The tube is exhausted of gas to a pressure so" low that conduction ofelectricity can occur between the cathode and the anode across thevacuous space operatively independent of positive gas ionization, asdescribed on pages 409 to 430 in the Physical Review for December, 1913.In exhausting the tube, traces of oxids, which are apt to give off gasduring the operation of the tube may be removed by introducing hydrogengas, heating the walls of the tube externally and then reexhausting tothe required low pressure, say, below 0.05 of a micron of mercurypressure.

When the tube is operated, the cathode 7 is heated to incandescence bypassage of current and a source of current of suitable voltage isconnected at its negative terminal to the cathode and at its positiveterminal to the anode housing 1 with which the target plate 15 is inelectrical contact. The electrons emitted by the cathode travel underthe influence of the electrical field to the anode where X-rays areproduced by their impact. The cathode rays are focused by theelectrostatic field of the ring 8 to strike a spot of limited area onthe target. Some of the X-rays are permitted to leave the tube throughthe window 19 so as to be available for use.

The electrons also charge the glass Wall of the tube to the full cathodepotential. Were the tube 6 absent, disruptive discharges would occur atthe joint 5 between the glass and the metal wall thereby disintegratingthe glass and allowing air to enter the tube,

The tube 6 projecting into the tube 2 past v the joint between the glassand metal preventsthe glass from becoming charged in the vicinit of theseal in the following manner: he first electrons entering the narrowspace between the tube 6 and the envelop wall charge the glass near theend of the tube 6 and the following electrons are repelled by thenegatively charged glass and are attracted by the positively chargedtube 6 so that few if any reach the joint 5.

The tube shown in Fig. 2 is very similar to the tube shown in Fig. 1,with the exception of the anode construction. The cathode rays strike ananode plate 20 consisting of thin metal, as platinum or silver, whereX-rays are generated which pass through the cooling fluid contained inan outer housing 21 and out through a-window 22 which may consist ofthin metal, for

' by Letters Patent of the United States, is

1. An electrical discharge device comprising the combination of anenvelop consisting of a conducting section and an insulating sectionsealed to each other, a cathode sealed into said insulating section,cooperating with said conductive section acting as anode, and areentrant tubular member connected to the conductive section of saidenvelop extending into the insulating section thereof,

spaced closely adjacent but out of contact with said envelop.

2. An electrical discharge device comprising the combination of anenvelop comprising a conductive section and an insulating section sealedto each other, a cathode sealed into said insulating section cooperatingwith said conductive section acting as anode, and conductive means forcarrying the anode potential into the insulating section of saidenvelop, said means being spaced closely adjacent but out of directcontact with said envelop.

3. An X-ray tube comprising the combination of an envelop comprising ametal section and an insulating section sealed to each other, aconductive member within said envelo joined to said metal section andexten ing spaced away from the envelop past the joint between-saidconductive and insulating sections, said tube being evacuated to apressure so low that conduction of electricity can occur by an electrondischarge substantially independent of positive ionization, a cathodeadapted to be operated at incandescence and a cooperating anode.

4. An electrical discharge device comprising the combination of anenvelop consisting in part of metal and in part of insulating material,said envelop being exhausted to a pressure so low that conduction ofelectricity can occur therein by an electron discharge operativelyindependent of positive ionization, a cathode operable at incandescence,an anode, and shielding means interposed between the cathode and thejoint between the parts of said. envelop for preventing the accumulationof an electric charge on theinsulating-section adjacent said joint. Inwitness whereof, I have hereunto set my hand this 12th day of June,1916.

WILLIAM D. COOLIDGE.

